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M2C > Transport across membranes I, II: Ion Gradients, Electrochemical Driving Forces, Membrane Potential > Flashcards

Transport across membranes I, II: Ion Gradients, Electrochemical Driving Forces, Membrane Potential Flashcards

1
Q

molecules/ions can only cross via

A

Transporters or channels that act as gates

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2
Q

where are transport systems located?

A

both the cell membrane and on the membrane of intracellular organelles

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3
Q

what electrically active cells depends on constant changes in ion fluxes? (action potential)

A

neurons, cardiomyocytes, and muscle cells

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4
Q

simple diffusion occurs through the ____________

A

lipid bilayer

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5
Q

describe diffusion through a Semi-Permeable Barrier

A
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6
Q

transport can be classified into which two categories?

A

active transport or passive transport (diffusion)

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7
Q

active transport can be classified into which two categories?

A

primary and secondary

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8
Q

secondary active transport happens via which two methods?

A

symports (same direction) and antiports (opposite directions)

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9
Q

diffusion can be classified into which two categories?

A

simple and facilitated

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10
Q

what type of transport does bulk flow derive from?

A

diffusion

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11
Q

simple diffusion happens via which two methods?

A

via bilayer and via ion channels

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12
Q

bulk flow is driven via which two methods?

A

hydrostatic pressure (force exerted by a fluid) and osmotic pressure (pressure required to prevent the flow)

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13
Q

What are the 3 modes of passive through the plasma membrane according to Fick’s First Law

A
  1. simple diffusion via lipid bilayer
  2. simple diffusion via ion channels
  3. facilitated diffusion with aid of carrier proteins
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14
Q

Is energy required for passive transport through the cell membrane?

A

No energy is required for passive transport.

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15
Q

what mode of transport does the cell invest energy to force ions/molecules to cross the membrane?

A

active transport

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16
Q

describe Brownian movement in diffusion via lipid bilayer

A

dictates chance spread from high concentration to the low concentration area, creating a homogenized, equalized average concentration & driven by thermal energy

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17
Q

what does a semi-permeable barrier consider changes in?

A

net flux of molecules across membrane as the concentration gradient changes

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18
Q

True or False: The two sides of the
membrane are parts of one continuous compartment

A

True

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19
Q

True of False: The compound randomly diffuses down its concentration gradient from low concentration to high concentration.

A

False.

from high concentration to low concentration

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20
Q

what is the driving force in diffusion through a semi-permeable barrier?

A

the concentration gradient

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21
Q

What happens to the net flux of molecules when there is a large initial concentration gradient?

A

A large initial concentration gradient creates a significant net flux of molecules from the side with higher concentration to the side with lower concentration.

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22
Q

How does the net flux change as the concentration gradient decreases?

A

As the concentration gradient decreases, the net flux of molecules also decreases.

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23
Q

What is the concentration on side 1 and side 2 during the intermediate stage of diffusion?

A

During the intermediate stage, the concentration on side 1 has decreased to 0.75 M, while the concentration on side 2 has increased to 0.25 M.

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24
Q

What happens to the net flux during the intermediate stage of diffusion?

A

The net flux decreases as the concentration gradient between the two sides decreases

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25
Q

What is the final state of concentrations on both sides of the membrane?

A

In the final state, the concentrations on both sides of the membrane become equal and the net flux becomes 0. This ensures a dynamic steady state

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26
Q

what determines how permeable the membrane is for a solute and how readily it diffuses across the bilayer?

A

the solubility of the solute in lipid

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27
Q

if the solute can cross, where does it go down?

A

its concentration gradient

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28
Q

define concentration gradient?

A

A concentration gradient is the difference in the concentration of a substance between two regions. It represents the gradual change in the concentration of solutes in a solution as a function of distance through a solution.

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29
Q

what does the permeability of the bilayer to different molecules depend on?

A

hydrophilic/hydrophobic nature

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30
Q

True or False: the hydrophobic molecule penetrates easily

A

True

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31
Q

How are hydration shells created?

A

Polar molecules associate with water molecules

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32
Q

The smaller the molecules the _____ polar it is and the more rapidly it diffuses across the bilayer.

A

the smaller the molecule, the LESS polar

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33
Q

lipids without proteins are….

A

highly impermeable to ions, no matter how small they are

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34
Q

Give examples of Hydrophobic molecules

A

O2, CO2, N2, steroid hormones (testosterone, progesterone, estrogen)

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35
Q

Give example of small uncharged polar molecules

A

H20, urea, glycerol, NH3

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36
Q

Give examples of large uncharged polar molecules

A

glucose, sucrose

37
Q

give examples of Ions

A

H+, Na+, HCO3-, K+, Ca2+, CI-, Mg2+

38
Q

if lipid solubility is high, does it create a strong or weak concentration
gradient across the
membrane?

A

strong concentration

39
Q

If the lipid solubility is high, does the molecule’s transfer accelerate or decelerate?

A

If lipid solubility is
high, the membrane,
accelerating the
molecule’s transfer.

40
Q

what does Fick’s Law describe?

A

passive movement molecules down its concentration gradient

41
Q

Fick’s Law Equation

A

Flux (J) (molecules per unit time) =

(C2 – C1) · (Area · Permeability coefficient) / Thickness

42
Q

what is the permeability coefficient ?

A

the mobility of the solute in the diffusion path

43
Q

What are the C2 and C1 in Fick’s Law ?

A

C2 is the higher concentration and C1
is the lower concentration

  • C2 - C1 = Concentration difference.
44
Q

what is the thickness in Fick’s Law?

A

the length of the diffusion path

45
Q

Simple diffusion through ion channels as well as facilitated diffusion with the aid of carrier proteins are mediated by what?

*Hint: the answer in in the question

A

proteins that function as gates

46
Q

True or False: All modes of transport follow Fick’s Law of Diffusion.

A

False.

Not all modes of transport follow Fick’s Law of Diffusion. Fick’s Law specifically applies to passive diffusion, where the movement of molecules is driven by a concentration gradient and does not require energy input.

47
Q

is diffusion via carrier proteins passive?

A

Yes, but solute transport is accelerated/
facilitated by the presence of
the carrier protein (compared
to unaided diffusion through
the membrane).

48
Q

What does the protein provide in both channels and carriers?

A

a permeation path

49
Q

How does diffusion through a channel/transporter facilitate the transport?

A

by making it less difficult energetically

50
Q

in simple diffusion, is peeling off the hydration shell lowly or highly energetic?

A

peeling off the hydration shell is highly energetic

51
Q

is the activation energy for delta G in diffusion through the bilayer low or high?

A

the activation
energy ΔG for diffusion through the bilayer is high

52
Q

True or False: A transporter protein reduces the delta G for transmembrane diffusion of the solute

A

True.

53
Q

How does a transporter protein reduce the delta G for transmembrane diffusion of the solute ?

A

by making the peel-off easier
- forming non-covalent
interactions with the dehydrated
solute to temporarily replace the
hydrogen bonding with water
- providing a hydrophilic
transmembrane passageway.

54
Q

describe facilitative transport

A

molecule binds to protein transporter and the mechanism/driving force is passive diffusion

  • momentary binding to protein transporter that makes transport saturable
55
Q

the molecule (substrate) is released to the other side due to ______ concentration

A

lower

56
Q

define carrier

A

a transmembrane protein that binds substrates on one side of a membrane and transports them to the other side

  • spontaneous conformational change
57
Q

define spontaneous conformational change

A

natural change in 3D shape of substrate/molecule

  • possesses 1+ binding sites specific for molecules of certain substances
58
Q

what happens when velocity of transport reaches maximum rate transport

A

it gets saturated

59
Q

how does simple diffusion differ from Facilitative transport

A
  • it does not require binding to a protein
  • the graph remains linear
  • no saturation
60
Q

in facilitated diffusion, saturation kinetics is due to …..

A

a finite # of carriers & the conformation changes

60
Q

in terms or kinetics, channels are ________, while carriers are ________.

A

channels are linear where carriers are saturable

61
Q

what causes saturation?

A

more solutes being transported than the transporters can handle

  • maxing-out of the increasing rate to a steady state rate (Vmax)
61
Q

do channels have a weak or strong interaction with the permeating compound? and is the permeation slow or fast?

A

weak interaction with permeating compound/molecule/substrate

  • very rapid permeation
  • no conformational changes
  • no saturation (simple diffusion)
62
Q

what are ionophores used for?

A

increasing permeability of membrane to specific ion

63
Q

what are ionophores?

A

small hydrophobic molecules

64
Q

what classes can ionophores be divided into?

A
  1. mobile ion carriers
    • Valinomycin –> K+
    • FCCP –> H+
    • A23187 –> Ca2+/Mg2
  2. synthetic channel formers
    • Gramicidin A)
65
Q

Sometimes a “cracked” transporter in facilitated diffusion can be used as a _______ in simple diffusion.

A

channel

66
Q

how do transporters get “cracked” in the first place?

A

they get stuck in a confirmation where a crack opens in the protein complex allowing selected ions to flow through
- so it works more as a channel

67
Q

give examples of “cracked” transporters

A

some glutamate transporters
- CFTR

68
Q

in terms of simple diffusion, it is driven by a _______ gradient

A

concentration

69
Q

in terms of Facilitated Diffusion and Ion Transport, they are driven by an ___________ gradient

A

electrochemical

70
Q

diffusion can ________ electrical gradient

A

generate

71
Q

What is a difference in electrical charge between 2 spots called?

A

Electrical Potential/ Voltage

72
Q

How do we measure electrical gradients?

A

in Volts

73
Q

What is Ohm’s Law?

A

Speed of flow (current) of electrical charge depends on the electrical concentration gradient (electrical potential) & properties of the flow path (resistance).

74
Q

What is Ohm’s Law?

A

I = V/R
V = I x R

I = current (amp)
V = electrical potential (volt)
R = resistance (R, Ohm , horse shoe looking ahh symbol)

75
Q

define membrane potential

A

net charge inside the cell - net charge outside the cell

76
Q

in most cases, the inside of the cell is slightly more ________.

A

negative

77
Q

The difference in charges establishes an _________________________.

A

electrical gradient

78
Q

When the chemical concentration is higher inside than outside, the direction of the chemical driving force is ____________.

A

outward

79
Q

when the chemical concentration is higher outside than inside, the chemical driving force is ____________.

A

inward

80
Q

in both cases, if permeable the molecules will move passively in the direction of the direction of the driving or…..

A

down the concentration gradient

81
Q

charged ions have what kind of force

A

electrical driving force

82
Q

on a positively charged ion, the direction of the electrical driving force is

A

inward

83
Q

the positive ion will go in,

A

down its electrical gradient

84
Q

the direction of the electrical driving force on a negatively charged ion is the _________ that of the positive ion.

A

opposite

85
Q

The direction of the electrical gradient depends both on

A

concentration and on the charge

86
Q

Do the two driving forces, chemical and electrical gradients, work dependently or independently?

A

independently

87
Q
A

M2C (11 decks)

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